Crystalline TiO2 Research Articles

Plasmonic Nanocrystal Assembly-Semiconductor Hybrids for Boosting Visible to Near-Infrared Photocatalysis.

Plasmonic metal-semiconductor hybrid photocatalysts have received much attention because of their wide light harvesting range and efficient charge carrier generation capability originating from plasmon energy transfer. Here, we introduce a plasmonic metal-semiconductor hybrid nanostructure consisting of a Au core-satellite assembly and crystalline TiO2. The formation of Au@TiO2-Au core-satellite assemblies using TiO2 as a spacer and the subsequent growth of outer TiO2 shells on the core-satellite assemblies, followed by calcination, successfully generated Au core-satellite assembly@TiO2 nanostructures. Exquisite control over the growth of the TiO2 interlayer enabled the regulation of the gap distance between the core and satellite Au nanocrystals within the same hybrid morphology. Due to the structural controllability of the present approach, the gap-distance-dependent plasmonic and photocatalytic properties of the hybrid nanostructures could be explored. The nanostructures possessing the most closely arranged Au nanocrystals showed high photocatalytic activity under visible to near-infrared light irradiation, which can be attributed to strong plasmon coupling between the core and satellite Au nanocrystals that can expedite the formation of intense plasmon energy and its transfer to TiO2.

Ag-doped hollow TiO2 microspheres for the selective photo-degradation of bilirubin

The surface of highly crystalline hollow TiO2 microspheres was nanostructured to contain recognition sites for bilirubin and simultaneously doped with Ag to achieve a photocatalytic response to visible light irradiation. The molecular imprinting technique was employed to obtain the recognition sites, whereas Ag-doping was tested either during the synthesis or after the complete synthesis by impregnation. Different Ag:Ti molar proportions were studied (1:2; 1:4 and 1:6). From the absorbance spectra in suspensions of the different microspheres, the ratio of 1:6 molAg/molTi was established as allowing for a greater capacity of absorption of visible light. It was possible to confirm a positive catalytic effect of Ag-doping, either with ultraviolet or visible light, especially for molecularly imprinted hollow microspheres doped during the synthesis. The increases in kinetic constants were much higher for molecularly imprinted hollow microspheres doped during the synthesis and calcined at 250 °C (12 min−1 and 9 min−1, for ultraviolet and visible light) compared to the corresponding undoped microspheres (8 min−1 and 5 min−1, for ultraviolet and visible light), leading to imprinting factors of 1.6 and 1.9, for ultraviolet and visible light, respectively. Selective photocatalysis was also confirmed with α values of 1.4 and 1.3 for ultraviolet and visible light, respectively. In conclusion, it was possible to obtain, with success, selective Ag-doped hollow TiO2 microspheres with a higher rate of bilirubin degradation compared to undoped hollow TiO2 microspheres, even with visible light irradiation.

Optimizing study on the NH3-SCR activity of Ce-W-Ti@g-C3N4 catalyst: Influence of graphite carbon nitride types

Herein, three g-C3N4(MCN/TCN/UCN), obtained by the direct pyrolysis of melamine/urea/thiourea respectively, were introduced as supports to optimize the NH3-SCR activity of Ce-W-Ti catalyst. Compared to CWT-400-Air, CWT@g-C3N4(2)-300-N2 exhibits lower crystalline anatase TiO2 and larger specific surface area, which improves the dispersion of Ce/W/Ti species on catalysts surface. Furthermore, the introduction of g-C3N4 as supports also contributes to doping C/N elements into Ce-W-Ti catalyst and increases the Ce3+/(Ce3++Ce4+) and Oα/(Oα+Oβ) molar ratios on catalyst surface. These all are advantageous to the NH3-SCR activity. However, UCN shows better promotional effect than MCN and TCN. This might be mainly attributed to the loose and porous stacked layered fold structure of UCN, the larger BET surface area, higher dispersion of Ce/W/Ti species and moderate weak/medium-strong acid sites of CWT@UCN(2)-300-N2. At the same time, the influence of carbon nitride amount, calcination atmosphere and calcination temperature on the NH3-SCR activity of CWT@g-C3N4 catalyst were also investigated.

Ethylene photocatalytic degradation using TiO2 immobilized in a NETmix mili-photoreactor

Ethylene oxidation by TiO2 photocatalysis was studied in a mili-photoreactor (NETmix), as a potential clean postharvest technology to scavenge ethylene from fruit. The NETmix photoreactor comprises a stainless steel slab imprinted with a network of cylindrical chambers interconnected by prismatic channels, sealed by a UVA transparent borosilicate slab (BS), and a UVA LED plate paced above the reactor window. A thin film of the photocatalyst was immobilized in the NETmix network or on the side of the borosilicate slab in contact with the ethylene gas stream. Ethylene oxidation in single-pass mode (continuous operation) was evaluated as a function of TiO2 crystallinity, TiO2 loading, radiant power, illumination mechanism, feed stream composition (ethylene and water concentration), and flow rate. The catalyst loading and deposition surface, and relative humidity (RH) of the feed stream strongly affected the ethylene conversion, mineralization, and reaction rate. Even under severe conditions (RH = 25% and Qfeed = 571 cm3 min−1 for the back side illumination), the NETmix removed at least 0.11 μmolethylene min−1. The high efficiency of the photocatalytic NETmix reactor allows the removal of ethylene from the storage system at the beginning of fruit ripening, the period of the highest gas production, enabling it to be used as a promising technology in controlling fruit ripening.

Understanding the prototype catalyst TiO2 surface with the help of density functional theory calculation

AbstractTitanium dioxide (TiO2) is one of the most technologically promising oxides with a broad range of catalytic and photocatalytic activities. Theoretical modeling, especially density functional theory calculations, has been extensively carried out to understand the geometric structure, electronic structure, reactivity, and reaction mechanisms of TiO2 systems, as well as to develop new catalysts with improved performances. This review summarizes the recent theoretical progress on the well‐defined surfaces of TiO2 crystalline, and focuses on the structures, adsorptions, and reactions on the surface and at the interface. The theoretical methods and models, surface defects, surface doping, water splitting and H2 evolution, methanol conversion, CO2 reduction and CO oxidation, SOx and NOx degradation, CH4 conversion, organic pollutant degradation, CH bond activation and CC bond formation, dye sensitization, as well as the applications of TiO2 in some other fields, have been discussed in detail.This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis Structure and Mechanism > Computational Matmandatory approximaterials Science Electronic Structure Theory > Density Functional Theory

TiO2-UV detection under different types of acids and rinsing process for films preparation

Titanium dioxide (TiO2) films were prepared by the sol–gel method under different types of acids. Effect of hydrochloric acid (HCl), nitric acid (HNO3) and nature-based solutions (NBS) under ultraviolet (UV) detection of films were investigated. Films were coated by dip coating on glass substrate. Moreover, TiO2 films were compared properties on water rinsing (Ri) and without rinsing (WRi) processes. The phase structure of prepared samples was characterized by means of X-ray powder diffraction (XRD). The results confirm that films were highly crystalline anatase TiO2 and free from other phases of titanium dioxide. For the optical property, the transmittance (%T) observed sharp rise in the violet-ultraviolet transition region and a maximum transmittance of ~80%. Photocurrents were measured under UV intensity of 260 mWcm–2 and DC bias voltage of -20 – 20 volts (V). The results observed that currents increased as bias voltage increased. Current - Voltage (I-V) curves observed different slopes under the different of acids and rinsing process. The photocurrent of TiO2-NBS-Ri was greater than TiO2-HCl-WRi and TiO2-HNO3-WRi of 10 and 20 times; respectively. These findings suggest that the significant effect of the acid and rinsing process on crystalline, morphological, optical, and electrical properties of nanostructured TiO2 films would be useful for applying the device in UV photoelectric detection.

Photoinduced properties of anodized Ti alloys for biomaterial applications

The photocatalytic properties of anodic oxides on a newly developed TiNbSn and commonly used Ti6Al4V alloys as biomaterials were investigated. The alloys were anodized in an electrolyte of sodium tartrate acid with H2O2 at a high voltage and the mechanism of the photocatalytic and antiviral activities was studied. The anodized TiNbSn and Ti6Al4V exhibited highly crystallized rutile TiO2 and poorly crystallized anatase TiO2, respectively. X-ray photoelectron spectroscopy analysis revealed the presence of oxides of the alloying elements in addition to TiO2. The anodized TiNbSn exhibited higher activities than Ti6Al4V, and electron spin resonance spectra indicated that the number of hydroxyl radicals (⋅OH) generated from the anodized TiNbSn was higher than that from the anodized Ti6Al4V. The results can be explained by two possible mechanisms: the higher crystallinity of TiO2 on TiNbSn than that on the Ti6Al4V reduces the number of charge recombination sites and generates abundant ⋅OH; charge separation in the anodic oxide on TiNbSn due to the electronic band structure between TiO2 and the oxides of alloying elements enhances photo activities. The excellent photoinduced characteristics of the anodized TiNbSn are expected to contribute to the safe and reliable implant treatment.

Precise Control of Broadband Light Absorption and Density of Ti3+ States in Sputtered Black TiO2 Thin Films

Defect‐rich black titanium dioxide (B‐TiO2) has been extensively studied over the past decade due to its enhanced photoelectrochemical efficiency compared to titanium dioxide (TiO2), which is known for its outstanding photocatalytic stability. So far, most of the B‐TiO2 material is obtained by hydrogenation of crystalline TiO2, resulting in a disordered outer layer of a few nanometers thickness. Recently, a new sputtering process has been introduced to produce B‐TiO2 thin films without the usage of hydrogen. Herein, the influence of the sputtering process on the creation of Ti3+ defect states within the films is discussed. Comprehensive optical, structural, and electronic studies of the thin film suggest that increasing the density of Ti3+ states enhances the conductivity of the films and results in increased and broadband light absorption. In addition, the new sputtering method can also be used to alter the density of the defect states in the film in a controlled manner, allowing the optical and electronical properties of the thin film to be changed in a precise and controllable way.

Synthesis of uniformly ordered single-crystalline TiO2 nanorods on flexible Ti substrate

With high conductivity and ionic mobility, one-dimensional (1D) titanium dioxide (TiO2) nanoarrays have attracted great interest in the photoanode of solar cells and the cathode of lithium-ion/sodium-ion batteries. However, the synthesis of TiO2 nanoarrays often requires highly toxic or corrosive solution circumstances. Meanwhile, the case that most TiO2 nanoarrays are grown on rigid conductive substrate can’t satisfy the demand for application in the space of complex shape. In this work, we developed a simple method to prepare highly ordered single crystalline rutile TiO2 nanorod arrays with high density on flexible metal Ti substrate in relatively weak acid solution, and the orientation of the nanorods were more uniform than those by other means ever before. Based on detailed analysis, an ion-assisted and concentration-limited epitaxial growth mechanism by H+ and is proposed for this uniformly ordered rutile TiO2 nanorod array. This work can promote the research and application of flexible solar cells and lithium-ion batteries, especially their integration.

Optical and structural properties of nanocomposites based on HMW‐PMMA reinforced by spherical and rod‐shaped titanium dioxide nanoparticles

AbstractThis work presents an investigation on the optical and structural properties of two series of nanocomposites based on the incorporation of spherical‐ (NDs) or rod‐shaped (NRs) semiconductive crystalline titanium dioxide (TiO2) nanoparticles (NPs) into an insulating amorphous polymethylmethacrylate (PMMA) matrix. The UV–visible absorbance and reflectance measurements reveal that the increase in TiO2 NP concentration within the polymer matrix reduces the forbidden band size for both NDs and NRs, leading to an improvement of the refractive index. SEM and TEM morphological characterizations were performed to investigate the size, size distribution and NPs dispersion within the polymeric matrix. The structural analyses performed by using X‐ray diffraction show peaks ascribed to the TiO2 crystalline structure while infrared (FT‐IR) spectra indicate the occurrence of interactions between nanofillers and the polymer chain of the host matrix.

Modeling the aqueous interface of amorphous TiO2 using deep potential molecular dynamics.

Amorphous titanium dioxide (a-TiO2) is widely used as a coating material in applications such as electrochemistry and self-cleaning surfaces where its interface with water has a central role. However, little is known about the structures of the a-TiO2 surface and aqueous interface, particularly at the microscopic level. In this work, we construct a model of the a-TiO2 surface via a cut-melt-and-quench procedure based on molecular dynamics simulations with deep neural network potentials (DPs) trained on density functional theory data. After interfacing the a-TiO2 surface with water, we investigate the structure and dynamics of the resulting system using a combination of DP-based molecular dynamics (DPMD) and abinitio molecular dynamics (AIMD) simulations. Both AIMD and DPMD simulations reveal that the distribution of water on the a-TiO2 surface lacks distinct layers normally found at the aqueous interface of crystalline TiO2, leading to an ∼10 times faster diffusion of water at the interface. Bridging hydroxyls (Ti2-ObH) resulting from water dissociation decay several times more slowly than terminal hydroxyls (Ti-OwH) due to fast Ti-OwH2 → Ti-OwH proton exchange events. These results provide a basis for a detailed understanding of the properties of a-TiO2 in electrochemical environments. Moreover, the procedure of generating the a-TiO2-interface employed here is generally applicable to studying the aqueous interfaces of amorphous metal oxides.

Electrospun TiO2 Nanofibers in the Presence of Avocado Seed Extract

The electrospinning technique is particularly prominent in membrane production techniques due to its easy applicability and ability to obtain nanofibers in various diameters with high surface area. Titanium dioxide (TiO2) is often used in biomaterial technologies due to their high biocompatibility, high processability and their photocatalytic activities in waste water treatment. In this study, TTIP (Titanium tetra isopropoxide) was used as a TiO2 precursor and PVP polymer was used as a carrier polymer for electrospinning. Avocado seed extract (ASE) which is a new and valuable source of phenolic compounds was used for the coordination and reduction of TTIP. TiO2-PVP-Avocado seed extract (T/P/A) composite nanofibers were produced at different voltages, distances and polymer concentrations. Crystalline TiO2 formation was not observed in as-spun nanofibers, thus selected nanofibers were heat treated at 500oC for 3 h. Smooth and integrated TiO2 nanofibers prepared by using 5 w% PVP, at 15 kV and 15 cm distance with or without ASE were imaged by Scanning Electron Microscopy (SEM). X-ray Diffraction (XRD) patterns of heat-treated TiO2 nanofibers prepared in the presence of ASE were crystallized mainly in anatase form. However, both anatase and rutile phases were obtained in the crystalline structure of TiO2 nanofibers when ASE was not used. Specific IR vibrations of TiO2 were shown by Fourier Transform Infrared Spectroscopy (FTIR). These green synthesized electrospun TiO2 nanofibers may have potential to be used in biomaterial and engineering applications.

Employing Ion-Beam Sputter Deposited TiO2 Buffer Layers for VO2-Related Devices

Vanadium dioxide (VO2) is considered to be the most promising material for thermochromic smart windows due to its insulator-to-metal transition causing an abrupt change of transmittance near ambient temperature. TiO2 buffer layers are expected to have a beneficial impact on the growth and performance of the functional VO2 thin film, as they may induce crystallinity at lower growth temperatures and act as a barrier layer for ion diffusion from glass substrates. However, a systematic evaluation of TiO2 buffer layers of different phases and thicknesses to assess potentially competing impacts is still lacking. Here, we grow TiO2 buffer layers by ion-beam sputter deposition (IBSD) at different substrate temperatures to obtain amorphous TiO2 as well as crystalline TiO2 in the anatase and rutile phase, respectively. We investigate the buffer layers themselves and shed light on how these buffer layers influence the performance of the functional VO2 layer grown on top by combining experimental and theoretical means. We find that the VO2||TiO2 interface is the most crucial part of the multilayer structure with an urgent need for minimum roughness. The two types of crystalline TiO2 buffers yield similar results in terms of optical performance; however, we find that only rutile buffer layers significantly relieve the growth conditions needed.

Photocatalytic performance assessment of Fe-N co-doped TiO2/β-cyclodextrin hybrid systems prepared by supercritical antisolvent micronization for organic dyes removal

This work aims to demonstrate that micronized β-cyclodextrin (β-CD) improves the photocatalytic activity of Fe-N-TiO2. Fe-N-TiO2/β-CD hybrid systems were employed in the photocatalytic removal of Acid Orange7 (AO7) and Methylene Blue (MB). The supercritical antisolvent process (SAS) was used to micronize β-CD at different pressures. The chemical-physical properties of the hybrid photocatalysts were detected through various characterization methods. Wide angle X-ray diffraction patterns evidenced the anatase as the typical TiO2 crystalline phase. FT-IR spectra showed interactions between β-CD and Fe-N-TiO2. The activity of photocatalysts in the degradation of AO7 and MB dyes was analyzed under UV and visible light irradiation. Fe-N-TiO2/β-CD120 photocatalyst led to the total UV light-driven discoloration of the AO7 aqueous solution. Instead, the Fe-N-TiO2/β-CD120 system allowed for achieving an MB discoloration kinetic constant under visible light higher than the AO7 discoloration kinetic constant. Reuse cycle tests proved that the Fe-N-TiO2/β-CD120 sample is a stable photocatalytic material.

Hydrothermal synthesis of carbon-coated mixed crystalline phase TiO2 nanoparticle carbon microsphere composites as high performance anode materials for Li-ion batteries

Hydrothermal synthesis of carbon-coated mixed crystalline phase TiO2 nanoparticle carbon microsphere composites as high performance anode materials for Li-ion batteries

Investigating the impact of TiO2 crystalline phases on catalytic properties of Ru/TiO2 for hydrogenolysis of polyethylene plastic waste

A series of TiO2-supported Ru catalysts with different TiO2 crystalline phases was synthesized and employed for the hydrogenolysis of polyethylene (PE). CO chemisorption, high-angle annular dark-field-scanning transmission electron microscopy, temperature-programmed reduction, and CO-Fourier transform infrared spectroscopy suggested that the degree of strong metal-support interactions (SMSIs) varied depending on the type of the TiO2 phase and the reduction temperature, eventually influencing the catalysis of PE hydrogenolysis. Among the synthesized catalysts, Ru/TiO2 with the rutile phase (Ru/TiO2-R) exhibited the highest catalytic activity after high-temperature reduction at 500 °C, indicating that a certain degree of SMSI is necessary for ensuring high activity in PE hydrogenolysis. Ru/TiO2-R could be successfully employed for the hydrogenolysis of post-consumer plastic wastes such as LDPE bottles to produce valuable chemicals (liquid fuel and wax) in high yields of 74.7%. This work demonstrates the possibility of harnessing the SMSIs in the design and synthesis of active catalysts for PE hydrogenolysis.

Photocatalytic antimicrobial and photostability studies of TiO2/ZnO thin films

A nanothin film-based antimicrobial coating has been attractive in response to the rise and spread of pathogenic microbes, which led to the development of low-cost, effective, and rapid disinfection methods for coating material. TiO2/ZnO bilayer thin films have been developed through magnetron sputtering and thermal oxidation. The influence of oxidation temperature on structural, optical, photocatalytic, photostability, and antimicrobial properties of Ti/ZnO thin films has been addressed. X-ray diffraction (XRD) analysis has shown the presence of hexagonal wurtzite ZnO, Ti0.895O.77, and anatase TiO2 in the bilayer films. Increasing the oxidation temperature reveals a certain degree of crystallization and transforms Ti0.895O.77 into the anatase/rutile TiO2 phase. The bottom layer of ZnO provides sufficient oxygen to improve TiO2 crystallinity and prevent transforming anatase to rutile during thermal oxidation process. Moreover, Ti/ZnO thermally oxidized at 550 °C exhibit excellent photocatalytic performance under UV irradiation with high photostability. The inhibition rate increased (p < 0.05) with irradiation time forE. coli,S. aureus, andC. albicans with effectiveness values reaching approximately 97 ± 3.408, 98 ± 2.409, and 95 ± 3.105 %, respectively. This work reveals that magnetron sputtering through a thermal oxidation approach could generate stellar TiO2/ZnO thin films as photocatalysts and antimicrobial agents with cost-effectiveness and efficiency.

Pt Single Atoms as Co‐Catalysts on CdS‐Sensitized Single‐Crystalline TiO2 Nanoflakes for Enhanced Visible Light Photocatalytic H2 Generation

AbstractStudies on single‐atom catalysts (SACs) with individually isolated metal atoms anchored on specific supports have gained great interest in photocatalysis due to their enhanced catalytic activity and optimal atom utilization. By providing an optimized number of active sites and enhancing their intrinsic activity, SACs afford a distinctive platform for photocatalysis at the atomic level. In this study, we investigate the photocatalytic H2 generation of Pt single atoms (SAs) anchored on CdS‐sensitized single crystalline anatase TiO2 nanoflakes (ATNF) in the visible spectral range. Vertically‐aligned ATNF were synthesized on fluorine‐doped tin oxide substrates by a hydrothermal process, which were further sensitized by CdS nanoislands (NIs) using the successive ionic layer adsorption and reaction (SILAR) technique. Finally, a reactive‐deposition approach was used to successfully anchor Pt SAs on CdS‐sensitized ATNF. Under optimized conditions, the highest photocatalytic H2 evolution on Pt‐anchored single atom CdS sensitized ATNF was 17.8 μL h−1 under visible light illumination, which is 15.8, 7.5, and 6.7‐fold higher than bare CdS/FTO, PtSA/CdS/FTO, and ATNF, respectively. Overall, the density of Pt SAs plays a vital role via strong trapping of the photogenerated electrons and significantly improves the efficiency of electron‐hole separation, making PtSA/ATNF efficient solar‐driven photocatalysts.

TiO2 aerogel composite high-efficiency photocatalysts for environmental treatment and hydrogen energy production

Abstract Photocatalysis is a new type of renewable energy technology used in environmental treatment and hydrogen energy production. In this regard, a new class of photocatalysts, TiO2 aerogels, are attractive for having the chemical characteristics of TiO2 nanomaterials such as high catalytic activity, good stability, non-toxic, and non-polluting, and the structural characteristics of aerogels such as large specific surface area, high porosity, the 3-dimensional interconnected network structure composed of relatively uniform nanoparticles, and high light transmittance. Here we review the recent progress in TiO2 aerogels for photocatalysis, focusing on preparation techniques, the crystalline phases’ influence on photocatalytic properties, the modification of photocatalytic properties, and the analysis and discussion of future development. In particular, we first summarize various preparation techniques, including sol–gel method, nanoparticles self-assembly synthesis, and high-temperature aerosol technique, then detail the structure and composition of TiO2 crystalline phases that affect the photocatalytic properties. Subsequently, we discuss strategies to further enhance the photocatalytic properties of TiO2 aerogels by the composite of SiO2 aerogel semiconductors, the doping of metal dopants, and the doping or composite of non-metallic substances, and elaborate the modification mechanism and the modification effect achieved. Finally, combined with the research status of TiO2 aerogels and the development experience of other aerogels, we conduct a reasonable analysis and discussion on their further research directions and industrialization roads.

Total Specific Energy as a New Figure of Merit for the Design of Porous TiO2 Surfaces Synthesized via Plasma Electrolytic Oxidation

The plasma electrolytic oxidation (PEO) is a variation of the anodic oxidation technique, one of the simplest and most economical methods to obtain crystalline and porous TiO2 coatings. Beyond the conventional approach of establishing a relationship between the variables of synthesis and the characteristics of the TiO2 coatings, a new figure of merit was defined in the present work for the synthesis of TiO2 coatings by PEO: the total energy per unit of surface (TSE). A strong relationship was found between TSE and the TiO2 anatase fraction. The application of TSE, together with the known influence of the variables of synthesis on the coating characteristics, allows a prediction, previously to the anodization and with reasonable precision, of the anatase fraction and the pore diameter of the coating. Applying the TSE new concept, three coatings were successfully designed. This is the first step toward a surface design using the PEO technique.